Have you contacted AWS and requested them to unblock port 25 so that you can run an email server? AWS requires this. @Bendo
The second issue - and this is absolutely the big issue. You have NOT requested AWS to set the rDNS (PTR record) for your MiaB instance. I am showing that it is:
ec2-52-63-192-134.ap-southeast-2.compute.amazonaws.com
but needs to be
box.goodlets.com
The third issue is that you’re trying to run a mail server on AWS … their IP ranges are blocked by many because of spammers. I am working with someone else right now to find a solution … and it looks like that solution may be an inexpensive SMTP relay that I have developed OR simply not using AWS for MiaB installations.